INHIBITION OF ODD OXYGEN PRODUCTION IN THE CARBON BOND 4 AND GENERIC REACTION SET MECHANISMS

Outdoor smog chamber experiments have been conducted by researchers in Australia at lower initial NO(x) and VOC-to-NO(x) ratios than those c hamber experiments which were used to formulate photochemical reaction mechanisms such as the Carbon Bond Four (CB4). When the Australians s imulated their experiments with CB4, they found that CB4 underpredicte d ozone production at low VOC-to-NO(x) ratios, i.e. in the NO(x)-rich region of the ozone isopleth diagram above the ridge line. CB4 predict s a significant NO(x) inhibition in this region whereas the empirical General Reaction Set (GRS) mechanism, which was developed by the Austr alian researchers to fit their data, does not. In this study, a mass b alance and process analysis technique is used to explain the origins o f the NO(x)-inhibition in CB4 simulations. The causes are determined t o be in the inorganic reactions of the CB4, which are believed to be b oth complete and well-known. The primary cause was a strong negative f eedback of new radical production from the photolysis of ozone which o ccurred because of the longer delay needed to oxidize the higher initi al NO. The CB4 mechanism could still be incorrect if it is missing a s trong radical source, for example, in the poorly understood aromatics chemistry. The GRS, which lacks representation of the inorganic proces ses responsible for NO(x)-inhibition, may be achieving its predictive accuracy by compensating errors. If this is true, then the GRS would b e unsatisfactory for ambient air use. Additional smog chamber experime nts at low VOC-to-NO(x) ratios and better characterization of the Aust ralian chambers are needed to resolve the discrepancy in CB4 and GRS p redictions.